"A long brown coat - a duster, I thought it was called."
Man Wearing a Duster
Public DomainMan Wearing a Duster - Credit: Mcumpston

 

A duster is an aptly named coat that was originally worn by horsemen over their clothing as protection against dust, hence the rider-friendly slit up the back.

Dusters are generally light garments, made from canvas or linen. They're loose, so as to fit comfortably over other clothing, and ankle length.